1. Field of the Invention
The invention is directed to a microscope, preferably a laser scanning microscope, with at least one detector for detecting sample light coming from a sample, wherein the detector is protected from excessively high light outputs by at least one shutter.
2. Description of Related Art
Microscopes of the type mentioned above generally have detectors, for example, but not exclusively, CCD sensors, photomultiplier tubes (PMTs) or avalanche photo diodes (APDs) for detecting sample light such as, for example, fluorescent light. Particularly when using detectors designed for detecting very low light outputs or when light outputs in excess of the dynamic range of the detectors can occur, shutters are often arranged in front of the detectors in the detection beam path of the microscope. The shutters serve to protect the detectors against damage or premature aging due to excessively high light outputs (light intensities) of the sample light or of extraneous light. Extraneous light includes all light which is not intended for detection and which, therefore, should not reach the detector.
Mechanical shutters (slides, flaps, or the like), acousto-optical or electro-optical components or liquid crystal elements can be used as shutters. The shutters are generally controlled by a control unit depending on the operating state of the microscope. For example, the shutters can be controlled in such a way that they only open the detection beam path when sample light is to be measured, and the detection beam path remains closed when changing the settings of the microscope (for example, when changing the objective, filter or sample).
However, in an arrangement of this kind excessive light output cannot be prevented from striking the detector after opening the detection beam path because the shutter is controlled independently from the light output and this light output can only be measured by the detector after the shutter is opened.
To remedy this problem, it is known to use additional detectors, so-called monitor diodes, to measure the light output in the detection beam path also when the detection beam path is closed by the shutter. An arrangement of this kind is described, for example, in DE10253609A1. In this case, a portion of the light output is coupled out of the detection beam path of a scanning microscope before the shutter by a beamsplitter and is directed to an additional detector (i.e., the monitor diode). If the light output measured by the monitor diode exceeds a predetermined value, the detection beam path is closed by the shutter in front of the detector.
The arrangement described in DE 10253609A1 has some drawbacks, particularly when low light outputs must be detected. As a result of the necessity of coupling a portion of the light output out of the detection beam path to the monitor diode, not all of the sample light coming from the sample reaches the detector. Therefore, the detecting efficiency of the microscope is reduced. Also, the use of acousto-optical or electro-optical components and liquid crystal elements as shutters is disadvantageous because they can likewise lead to an attenuation of the light output to be detected and are more cost-intensive than mechanical solutions.